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Stinging nettles (Urtica dioica)



stining nettles
Since nettles are common plants, produce unattractive flowers and have the capability of inflicting an uncomfortable rash, it is not surprising we tend to avoid or ignore them. Actually they have several features that make them interesting and deserving of our attention.
To begin with, how do they manage to inject their venom? Each sting is made of one very large stiff cell, supported on a cushion of smaller cells (which provide flexibility), making a hair that is specialised for delivering a small dose of irritating chemicals under the skin. The end of the hair has a minute rounded tip, but this breaks off at the slightest touch leaving a sharp end like the point of a syringe needle. The silica strengthening makes it capable of puncturing the skin, and allows the cell contents containing the toxins to penetrate the wound.


leaf with stingssting drawing


The flowers of stinging nettles are inconspicuous since pollination is carried out by wind and there is no need for showy petals to attract insects. The strings of flowers dangle near the top of the plant where they will easily catch the wind. Plants are either male or female, and since they spread by the growth of rhizomes, a large patch may be of one sex only. You may have to walk some way to find plants of the other sex. What makes the mechanism special is the way the males launch their pollen.

                                              male stinging nettle

The tiny flower is encased in 4 sepals which stay sealed even when the anthers mature and release pollen. The anther stalks keep growing within the sealed bud, gradually building up a pressure which finally is released explosively, sending a puff of pollen into the air currents. This often happens on a warm day, and the ‘pop’ can just be heard if you are close enough. With a hand lens you can easily see the exploded flowers with their emptied anthers sticking out twice the length of the sepals that held them.
               
 The female flowers look like little bright stars. These are the minute bristly white stigmas, exposed to pick up the pollen in the wind to achieve fertilisation.
                              
Where man is concerned stinging nettles have beeen put to so many uses it is difficult to do more than just outline some of them. The phloem fibres from nettles can be extracted to make textiles and are prepared in a similar way to flax. There are numerous claims for the medicinal properties of the nettle both in ancient folk remedies and modern investigations for drug treatments. Yellow dyes can be made from the roots and green dyes from the leaves.Nettles can also be eaten; the leaves have a high protein content and are rich in certain minerals and vitamins. Cooking destroys the toxic substances and the leaves are supposed to taste similar to spinach. Cordials too can be made from the nettle. In the garden, nettles can be useful in composting because of their mineral content and because they act as accelerators. Nettles have a prominent place in our literature, folklore and customs. A quick surf of the internet will yield much more.
Stinging neetles are an important ecologically, helping to maintain the biodiversity. They are a component of the diet of several moths, the exclusive food plant for the caterpillars of the peacock and the small tortoiseshell butterfies. They are useful as indicator species since they are likely to occur where ground has been disturbed and is rich in nitrogen and phosphorus.

Jay (Garrulous glandarius)

Jays are a woodland bird, and can be observed at various locations along the Nickey Line, such as at Yew Tree Wood, in the cutting by Thumpers at Hemel Hempstead, by Knott Wood, and behind Ambrose Lane in Harpenden. This shy bird of the crow family is often found in small family groups, and is readily identified by the white rump as it flies off, although at close quarters the beautiful blue and black wing feather stands out. This feather was sought after as a lure for fly fishing, leading to the bird's persecution in the past.

The scientific name for the bird captures two key habits,  garrulous describing the loud screaming call of the bird, and glandarius relating to the Latin name for acorns, which the Jay buries during the autumn, for retrieval later in the winter when food is in short supply. Research has shown Jays can remember the location of over a thousand buried acorns!

                                      Jay

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Fungal Foray Wednesday 22 October 2008

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